B allomorph

The C type structure, or so-called C polymorph, is a combination of the A and B crystalline form [9], The A allomorph (60% of the total polymorph) is mainly located in the outer part of the granules whereas the B allomorph (40% of the total polymorph) is mainly located in the inner part of it [10],... 

Conditions required to generate A- and B-type crystal conformations are reasonably well-understood. Under cool, wet conditions (such as in a potato tuber), B-type starch crystals form, while in warmer, drier conditions (e.g. in a cereal grain), the A allomorph is preferred. Chain length also affects the selection of crystal form, chains of DP <10 do not crystallize, chains with a DP from 10 to 12 tend to form A-type crystals, and chains with a DP >12 tend to yield the B form.37,38 This is likely the result of differences in loss of entropy on crystallization experienced by chains of different lengths.39 An irreversible transition from B-type starch to A-type starch can be accomplished under conditions of low humidity and high temperature. This so-called... 

Prepn of a third allomorphic form, e-Fe203 Schrader, Butt -ner, Z. Anorg, Allgem. Chem. 328, 220 (1963) Trautmann, Forestier, CompL Rend. 261, 4423 (1965). Color and appearance of Fe203 are dependent upon the size and shape of the particles and the amount of combined water. Preparation and properties Gmelin s, Iron (8th ed.) 59, part B,... 

Figure 10 indicates that (a) If tvrc) allomorphs coexist in the Cladophora cellulose, the T behavior of both allomorphs is the same, (b) If the reduction of intensity in the T ... 

Fig. 1 X-ray diffractograms of the allomorphs in cellulose I family by the reflection method (the reflection plane is parallel to the membrane surface). A I, valonia cellulose, B IVj prepared from A through IIIi(C), C IIIi prepared from valonia.

Fig. 5 IR spectra of the deuterated allomorphs in OD stretching region. A I, valonia cellulose, B IV prepared from IHi (C), C IHi from A, D II, ophane, E Hn from D, F IVxi E.

Heating cellulose III in glycerol for 20 minutes at 260 °C yields cellulose IV and the two allomorphs IVi and IVn originate from cellulose I and II, respectively. The conversions are never totally complete, which explains the diffrculties in the production of good-quality X-ray diffraction patterns. However, unit-cell dimensions have been obtained for the two allomorphs of which IVi has a = 8.03 A, b = 8.13 A, c = 10.34 A, which is close to those found for form IVn = 7.99 A, b = 8.10 A, c = 10.34 A. ° In both instances the poor quality of the diffraction patterns does not allow determination of the space group. The authors suggest space group Pi, but this is not compatible with the proposed unit-cell dimensions. 

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